In recent years, as a new form of a power generation system, a fuel cell system has been proposed. The fuel cell system has many advantages that it is capable of easily implementing small-capacity and distributed power generation, is suitable for use in in-house power generation in each facility, does not generate harmful substances such as NOx and SOx, generates a low noise, and is applicable to cold districts.
Patent Literature 1 discloses such an exemplary configuration of the fuel cell system 1. Specifically, the fuel cell system disclosed in Patent Literature 1 includes a fuel cell main body, a fuel gas generating device, an air supply unit (air blower), an electric power converter (inverter), a heat recovery device, etc. Among these devices, the fuel gas generating device generates a hydrogen gas from a natural gas which is a raw material gas, and the air supply unit supplies oxygen to a fuel cell. The fuel cell generates electric power through an electrochemical reaction between the hydrogen gas and the oxygen. The electric power converter converts an electric energy generated in the fuel cell into a voltage and a frequency which are the same as those of electric power in a commercial power utility. The heat recovery device recovers heat generated in the fuel cell and the fuel gas generating device by a heat exchanger built into the heat recovery device and supplies the heat to another outside device which utilizes exhaust heat. Patent Literature 1 teaches that an electric motor for actuating the air supply unit is cooled by the air introduced by the air supply unit.
By the way, in cases where the fuel cell system is used in cold districts, there may be a possibility that water (e.g., water within a fuel cell stack) used within the system is frozen. This will be described more specifically. In the fuel cell system, it is necessary to take in air required for power generation from outside of a casing. In some cases, the interior of the casing of the fuel cell system is ventilated by the air taken in from outside. If an attempt is made to cover electric power and hot water consumed at home by electric power and hot water generated in the fuel cell system, the fuel cell system must be operated continuously for a long period of time, which reduces durable years (expected lifetime) of the system. To avoid this, typically, the fuel cell system is deactivated (stopped) during a nighttime when a consumption amount of the electric power and a consumption amount of the hot water at home are less, while the fuel cell system is activated (started-up) in early morning when the consumption amount of the electric power and the consumption amount of the hot water at home start increasing.
However, throughout the year, the fuel cell system installed in an outdoor location is forced to be operated under an outside air temperature in a range of, for example, a temperature lower than 0 degrees C. to about 40 degrees C. Because of this, especially in a case where the fuel cell system is activated in early morning in the deactivated state during a nighttime in a winter season, water inside a water tank and water within a water pipe in the fuel cell system may be frozen, which causes a trouble in an operation of the fuel cell system.
To address the above stated problem, Patent Literature 2 discloses that a sheath heater for heating an entire fuel cell system is provided. FIG. 6 is a block diagram showing a schematic configuration of a fuel cell system according to a prior art disclosed in Patent Literature 2. As shown in FIG. 6, a fuel cell system 100 includes a plate-shaped mount plate 102 in an internal space of a casing 101. On and above the mount plate 102, internal devices including a PEFC stack 103 are mounted. The mount plate 102 is provided with legs. Therefore, the mount plate 102 is placed to be spaced apart from an inner bottom surface of the casing 101. Between the inner bottom surface of the casing 101 and the mount plate 102, a sheath heater 104 for heating the internal space of the casing 101 is provided.
Patent Literature 3 and Patent Literature 4 disclose a means for heating the entire fuel cell system for the purpose of anti-freezing. For example, in Patent Literature 3, a cooling air inlet opening is provided at a lower portion of a casing accommodating a fuel cell, and a blower attached on a lower portion of the interior of the casing is actuated to take in outside air through the opening and supply the air to the fuel cell (see paragraph 0016, 0020). Patent Literature 3 discloses that in a low-temperature condition, a surface heater heats the lower portion of the casing to increase a temperature of the entire casing (see paragraph 0022). Patent Literature 4 also discloses that a heating means for heating the entire fuel cell system is provided (see, for example, Claim 1).
There is a fuel cell system in which an air pump of a diaphragm type is used as an air supply unit. Patent Literature 5 and Patent Literature 6 disclose a general technique about the air supply unit of the diaphragm type.